Efforts have been made in the past to recycle disposable diapers and other used sanitary products. In order to recycle used sanitary products, the used sanitary product is normally degraded in water followed by separating into constituent components of the sanitary product and recovering those constituent components. However, in addition to increasing in mass as a result of absorbing water, superabsorbent polymers contained in sanitary products also lose fluidity as a result of forming a gel, thereby lowering the processing capacity of processing devices.
Therefore, Japanese Unexamined Patent Publication No. 2009-183893 (Patent Document 1) discloses that superabsorbent polymer present in a used disposable diaper that has absorbed water is dehydrated with lime (claim 2). As a result, in addition to reducing the weight of the superabsorbent polymer, since fluidity is recovered as a result of returning to its original state from a gel, decreases in processing capacity of the processing device are avoided (paragraph [0020]).
In addition, Japanese Unexamined Patent Publication No. 2010-59586 (Patent Document 2) discloses a method for recycling used diapers wherein, in recycling a used disposable diaper, the superabsorbent polymer contained in the disposable diaper can be put into the form of fine particles without using chemicals. In this recycling method, the used disposable diaper is separated into a pulp component and a non-pulp component together with breaking up the used disposable diaper, and after washing a mixture of the degraded pulp component and vinyl or other non-pulp component with water, the non-pulp component is separated and recovered from the mixture, and superabsorbent polymer present in the pulp component, from which non-pulp component has been removed and which has absorbed water and swollen, is broken up into fine particles measuring 10 μm or less by a pulverizer without breaking up the fibers of the pulp component to form a suspension containing the fine particulate superabsorbent polymer, pulp component and water, followed by dehydrating the suspension and removing the superabsorbent polymer from the pulp component together with the water to recover the pulp component (claim 1). Patent Document 2 further discloses that, in a weighing step, the used disposable diaper is sterilized and deodorized using an ultraviolet lamp and ozone (gas) or ozone water and the like (paragraph [0015]).